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Synthesis and crystal structures of Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52
ARTICLE IN PRESS
Journal of Solid State Chemistry 179 (2006) 891–897 www.elsevier.com/locate/jssc
Synthesis and crystal structures of Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 Vasyl I. Zarembaa, Vitaliy P. Dubenskiya, Ute Ch. Rodewaldb, Birgit Heyingb, Rainer Po¨ttgenb, a
Inorganic Chemistry Department, Ivan Franko National University of Lviv, Kyryla and Mephodiya Street 6, 79005 Lviv, Ukraine b Institut fu¨r Anorganische und Analytische Chemie, Universita¨t Mu¨nster, Corrensstrasse 36, D-48149 Mu¨nster, Germany Received 26 October 2005; received in revised form 6 December 2005; accepted 10 December 2005 Available online 20 January 2006
Abstract The rare earth-platinum-indides Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 were synthesized from the elements by arcmelting of the components. Single crystals were grown using special annealing sequences. The three indides were investigated by X-ray powder and single crystal diffraction: Tb6Pt12In23 type, C2/m, Z ¼ 2, a ¼ 2811:9ð6Þ, b ¼ 441:60ð9Þ, c ¼ 1486:6ð3Þ pm, b ¼ 112:10ð3Þ1, wR2 ¼ 0.0629, 3645 F2 values, 126 variables for Nd6Pt13In22, a ¼ 2821:9ð6Þ, b ¼ 443:06ð9Þ, c ¼ 1481:0ð3Þ pm, b ¼ 112:39ð3Þ1, wR2 ¼ 0.0543, 3679 F2 values, 127 variables for Sm6Pt12.30In22.70, and a ¼ 2818:5ð6Þ, b ¼ 439:90ð9Þ, c ¼ 1480:9ð3Þ pm, b ¼ 112:29ð3Þ1, wR2 ¼ 0.0778, 3938 F2 values, 127 variables for Gd6Pt12.48In22.52. Most platinum atoms in these structures have a distorted trigonal prismatic coordination by rare earth metal and indium atoms. Together, the platinum and indium atoms build up a complex threedimensional [Pt12+xIn23x] polyanionic network in which the rare earth metal atoms fill distorted pentagonal and hexagonal channels. The 2c Wyckoff site in these structures plays a peculiar role. This site is occupied by indium in the prototype Tb6Pt12In23, while platinum atoms fill the 2c site in Nd6Pt13In22, leading to a linear Pt3 chain with Pt–Pt distances of 275 pm. The crystals with samarium and gadolinium as rare earth metal component show mixed Pt/In occupancies. r 2005 Elsevier Inc. All rights reserved. Keywords: Intermetallic compounds; Crystal structure; Indium
1. Introduction High-quality single crystals of indium-rich (more than 50 at% per formula unit) rare earth (RE)-transition metal (T)-indides can be grown via indium flux techniques. Either the elements are reacted directly with an excess of indium, or a precursor alloy is re-crystallized from liquid indium via a special temperature program. The excess indium can softly be removed with diluted acetic acid. An overview on the different compounds and metal flux techniques is given in [1] and [2]. In the RE–Pt–In systems, the indium-rich compounds REPtIn3 (RE ¼ La, Ce, Pr, Nd, Sm) [3], RE3Pt4In12 Corresponding author. Fax: +49 251 83 36002.
E-mail addresses: [email protected] (V.I. Zaremba), [email protected] (R. Po¨ttgen). 0022-4596/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2005.12.022
(RE ¼ Gd, Tb) [4], RE3Pt4In13 (RE ¼ La, Ce) [5], Dy2 Pt7In16 and Tb6Pt12In23 [6], LaPtIn4 and YbPtIn4 [3,7], and RE4Pt10In21 (RE ¼ La, Ce, Pr, Nd) [8] have been synthesized via the indium-flux technique or through special annealing procedures. All these compounds have complex crystal structures, where the platinum and indium atoms build up three-dimensional polyanionic networks. Within the polyanionic networks, the platinum atoms are well separated from each other. The shortest Pt–Pt distances observed are in Gd3Pt4In12 (338 pm) [4] and Tb6Pt12In23 (320 pm) [6], however, these Pt–Pt distances are considerably longer than the Pt–Pt distance of 277 pm in fcc platinum [9]. Further phase analytical investigations in the RE–Pt–In systems revealed a peculiar crystal chemical situation for the Tb6Pt12In23 structure type. The 2c In3 site can also be occupied by platinum (leading to a Pt3 cluster unit) or one observes Pt/In mixing. Both
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Table 1 Lattice parameters of the monoclinic indides RE6Pt12+xIn23x Compound
a (pm)
b (pm)
c (pm)
b (deg)
V (nm3)
Ref.
Nd6Pt13In22a Nd6Pt13In22 Sm6Pt12.30In22.70a Sm6Pt12In23 Gd6Pt12.48In22.52a Gd6Pt12In23 Tb6Pt12In23
2811.9(6) 2812.7(5) 2821.9(6) 2820.5(5) 2818.5(6) 2814.2(3) 2834.6(4)
441.60(9) 441.7(1) 443.06(9) 443.3(1) 439.90(9) 437.82(6) 440.05(7)
1486.6(3) 1487.2(3) 1481.0(3) 1480.7(3) 1480.9(3) 1479.9(1) 1477.1(3)
112.10(3) 112.11(2) 112.39(3) 112.36(1) 112.29(3) 112.035(9) 112.37(1)
1.7104 1.7119 1.7121 1.7121 1.6990 1.6902 1.7038
This This This This This This [6]
a
work work work work work work
Single crystal data.
Table 2 Crystal data and structure refinement for RE6Pt12+xIn23x (RE ¼ Nd, Sm and Gd) with Tb6Pt12In23-type structure, space group C2/m; Z ¼ 2 Empirical formula
Nd6Pt13In22
Sm6Pt12.30(1)In22.70(1)
Gd6Pt12.48(1)In22.52(1)
Molar mass (g/mol) Unit cell dimensions Calculated density (g/cm3) Crystal size (mm3) Detector distance (mm) Exposure time (min) o range; increment Integr. param. A, B, EMS Transm. ratio (max/min) Absorption coefficient (mm1) F(000) y range (deg) Range in hkl Total no. reflections Independent reflections Reflections with I42sðIÞ Data/parameters Goodness-of-fit on F2 Weighting schemea
5927.65 Table 1 11.51 15 15 170 70 8 24–1661; 1.01 14.0; 4.0; 0.012 5.12 76.3 4904 3–34 43/+25, 76, 722 8537 3645 (Rint ¼ 0.0490) 2873 (Rs ¼ 0.0515) 3645/126 0.942 a ¼ 0.0296 b¼0 R1 ¼ 0.0326 wR2 ¼ 0.0595 R1 ¼ 0.0495 wR2 ¼ 0.0629 0.00045(1) 2.66/3.73
5964.31 Table 1 11.57 15 20 80 70 12 0–1801; 1.01 14.5; 4.5; 0.012 6.67 77.4 4928 3–34 743, 76, 722 11 660 3679 (Rint ¼ 0.0670) 2552 (Rs ¼ 0.0781) 3679/127 0.889 a ¼ 0.0157 b¼0 R1 ¼ 0.0362 wR2 ¼ 0.0488 R1 ¼ 0.0710 wR2 ¼ 0.0543 0.000235(7) 2.91/4.74
6005.71 Table 1 11.74 15 15 140 70 5 0–1801; 1.01 13.5; 3.5; 0.012 7.72 79.3 4952 3–35 744, 76, 723 12 855 3938 (Rint ¼ 0.0652) 3266 (Rs ¼ 0.0530) 3938/127 1.001 a ¼ 0.0397 b¼0 R1 ¼ 0.0367 wR2 ¼ 0.0734 R1 ¼ 0.0485 wR2 ¼ 0.0778 0.00041(2) 3.33/–5.83
Final R indices [I42sðIÞ] R indices (all data) Extinction coefficient Largest diff. peak and hole (e/A˚3) a
Weight ¼ 1/[s
2
(F2o)+(aP)2+bP] where P ¼ 1=3 max (0, F2o)+2/3 F2c .
situations have been observed in the indides Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52. The synthesis, structure refinements, and crystal chemistry of these compounds are reported herein. 2. Experimental 2.1. Synthesis Starting materials for the preparation of Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 were ingots of the rare earth metals (Kelpin, Chempur or Johnson-Matthey), platinum powder (ca. 200 mesh, Degussa-Hu¨ls), and
indium tear drops (Johnson-Matthey), all with stated purities better then 99.9%. In the first step the larger rare earth ingots were cut into smaller pieces under paraffin oil. They were subsequently washed with n-hexane and kept under argon atmosphere prior to use. The paraffin oil and n-hexane were dried over sodium wire. The argon was purified before over titanium sponge (900 K), silica gel, and molecular sieves. The rare earth pieces were then arc-melted to small buttons under an argon atmosphere of ca. 600 mbar argon in a small arc-melting furnace [10]. Subsequently, the melted rare earth buttons were mixed with coldpressed pellets of the platinum powder and pieces of
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the indium tear drops in the ideal 6:12:23 or 6:13:22 atomic ratios and arc-melted. Each sample was re-melted three times in order to ensure good homogeneity. Weight losses after the melting procedures were always smaller than 0.5 wt%. After the arc-melting procedure the RE6Pt12In23 indides were obtained only as polycrystalline powders. Single crystals were grown using special heat treatment. First, the alloys were powdered and cold-pressed into pellets. Next, the samples were put in small tantalum containers that have been sealed in evacuated silica tubes as an oxidation protection. The ampoules were first heated to 1300 K for the Nd compound (to 1320 K for the Sm and Gd compounds) within 6 h and held at that temperature for another 6 h. Subsequently, the temperature was lowered at a rate of 4 K/h to 900 K for the Nd compound (to 920 K for the Sm and Gd compounds), then at a rate of 10 K/h to 700 K, and finally cooled to room temperature within 10 h. After cooling, the samples could easily be separated from the tantalum container. No reaction of the samples with tantalum could be detected. The brittle samples were all stable in air as compact pieces as well as fine-grained powders. The needle-shaped single crystals exhibit metallic luster. 2.2. X-ray powder diffraction The indides were investigated via Guinier powder patterns (imaging plate technique, Fujifilm BAS-1800) using CuKa1 radiation and a-quartz (a ¼ 491.30, c ¼ 540.46 pm) as an internal standard. The monoclinic lattice parameters (Table 1) were obtained from leastsquare fits of the Guinier powder data using a selfwritten computer program. The indexing of the complex powder patterns was facilitated through intensity calculations [11] using the positional parameters of the structure refinements. The lattice parameters determined from the powders and the single crystals showed reasonable agreement within two combined standard uncertainties. The course of the lattice parameters with respect to the rare earth metal component is discussed below. 2.3. Scanning electron microscopy The crystals investigated on the diffractometer have been analyzed in a scanning electron microscope (LEICA 420i) through energy dispersive analyses of X-rays using NdF3, SmF3, GdF3, platinum metal, and InAs were used as standards. No impurity elements heavier than sodium have been observed. The experimentally determined compositions of 1472 at% Nd:3372 at% Pt:5372 at% In for Nd6Pt13In22 (14.6:31.7:53.7), 1572 at% Sm:3072 at% Pt:5572 at% In for Sm6Pt12.3In22.7 (14.6:30.0:55.4), and 1572 at% Gd:3072 at% Pt:5572 at% In for Gd6Pt12.48In22.52 (14.6:30.4:55.0) were close to the compositions calculated from the structure refinements (in
893
parentheses). The uncertainties of the measurements of 72 at% arise from the irregular surface of the single crystals. 2.4. Structure refinements Needle-shaped single crystals of the three indides were selected from the crushed samples and examined on a Buerger precession camera (white Mo radiation, Fujifilm BAS-1800 imaging plate system) in order to check the quality. The intensity data sets were recorded in oscillation mode by use of a Stoe IPDS-II diffractometer with graphite monochromatized MoKa radiation. The absorption corrections for these crystals were numerical (X-Shape/X-Red). All relevant crystallographic data and experimental details for the data collections are listed in Table 2. The close structural relationship of the three new compounds with the Tb6Pt12In23 type was already evident from the X-ray powder data. Analyses of the diffractometer data sets were compatible with space group C2/m. The atomic parameters of Tb6Pt12In23 [6] were taken as starting values and the structures were refined with SHELXL-97 (full-matrix least-squares on F2) [12] with anisotropic displacement parameters for all atoms. The refinements revealed very small equivalent isotropic displacement parameters for the 2c Wyckoff site, indicating a larger scattering power. From a crystal chemical point of view, it is only possible to substitute the indium atoms of the Tb6Pt12In23 type by platinum. Refinement of the occupancy parameters of the 2c sites revealed full platinum occupancy for the neodymium crystal and Pt/In mixing for the samarium and the gadolinium crystals, leading to the refined compositions Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 for the crystals investigated. The final difference Fourier syntheses were flat for all three data sets (Table 2). The highest residual peaks were close to the platinum sites and most likely resulted from incomplete absorption corrections of these highly absorbing compounds. The positional parameters and interatomic distances of the refinements are listed in Tables 3 and 4. Further data on the structure refinements are available.1 3. Discussion The three new indides Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 have a close structural relationship with the recently reported structure of Tb6Pt12In23 [6]. As an example we present a projection of the Nd6Pt13In22 structure onto the xz plane in Fig. 1a. The unit cell is formed by two identical networks situated 1 Details may be obtained from: Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany), by quoting the Registry Nos. CSD–415864 (Nd6Pt13In22), CSD–415865 (Sm6Pt12.30In22.70), and CSD–415866 (Gd6Pt12.48In22.52).
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Table 3 Atomic coordinates and isotropic displacement parameters (pm2) of RE6Pt12+xIn23x (RE ¼ Nd, Sm and Gd) Atom
Wyck. Occ.
x
y z
Ueq
Nd6Pt13In22 Nd1 Nd2 Nd3 Pt1 Pt2 Pt3 Pt4 Pt5 Pt6 Pt7 In1 In2 In4 In5 In6 In7 In8 In9 In10 In11 In12
4i 4i 4i 4i 4i 4i 4i 4i 4i 2c 4i 4i 4i 4i 4i 4i 4i 4i 4i 4i 4i
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
0.45324(3) 0.82120(3) 0.83717(3) 0.25147(2) 0.38141(2) 0.32036(2) 0.90101(2) 0.96735(2) 0.39324(2) 0 0.40842(4) 0.71263(4) 0.76225(4) 0.14323(4) 0.04265(4) 0.94468(4) 0.32556(4) 0.87577(4) 0.47078(4) 0.43497(4) 0.72748(4)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.30004(5) 84(1) 0.91931(5) 82(1) 0.46918(5) 81(1) 0.36333(3) 79(1) 0.84816(3) 83(1) 0.08900(3) 78(1) 0.36453(3) 95(1) 0.13891(4) 95(1) 0.63812(3) 83(1) 1/2 161(2) 0.04752(6) 78(2) 0.43517(6) 76(2) 0.08371(6) 77(2) 0.28181(6) 84(2) 0.33970(7) 90(2) 0.93590(6) 92(2) 0.27999(6) 102(2) 0.16870(6) 80(2) 0.82143(6) 88(2) 0.49771(6) 95(2) 0.24700(6) 83(2)
Sm6Pt12.30(1)In22.70(1) Sm1 Sm2 Sm3 Pt1 Pt2 Pt3 Pt4 Pt5 Pt6 Pt7 In1 In2 In3 In4 In5 In6 In7 In8 In9 In10 In11 In12
4i 4i 4i 4i 4i 4i 4i 4i 4i 2c 4i 4i 2c 4i 4i 4i 4i 4i 4i 4i 4i 4i
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.30(1) 1.00 1.00 0.70 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
0.45384(3) 0.82103(3) 0.83509(3) 0.25192(2) 0.38150(2) 0.32044(2) 0.90060(2) 0.96696(2) 0.39235(2) 0 0.40768(4) 0.71267(4) 0 0.76219(4) 0.14465(4) 0.04421(4) 0.94407(4) 0.32552(4) 0.87620(4) 0.47191(4) 0.42752(5) 0.72735(4)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.30123(6) 0.92033(6) 0.46980(6) 0.36348(4) 0.84887(4) 0.09017(4) 0.36520(4) 0.13908(5) 0.64141(4) 1/2 0.04810(8) 0.43431(8) 1/2 0.08352(8) 0.28019(8) 0.33298(8) 0.93705(8) 0.28111(8) 0.16946(8) 0.82561(8) 0.49530(9) 0.24589(8)
95(2) 93(2) 104(2) 87(1) 88(1) 89(1) 106(1) 103(1) 98(1) 138(5) 89(2) 90(1) 138 88(2) 91(2) 114(2) 99(2) 117(2) 93(2) 94(2) 165(3) 91(2)
Gd6Pt12.48(1)In22.52(1) Gd1 Gd2 Gd3 Pt1 Pt2 Pt3 Pt4 Pt5 Pt6 Pt7 In1 In2 In3 In4 In5
4i 4i 4i 4i 4i 4i 4i 4i 4i 2c 4i 4i 2c 4i 4i
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.48(1) 1.00 1.00 0.52 1.00 1.00
0.45386(2) 0.82141(2) 0.83570(2) 0.25268(2) 0.38104(2) 0.32048(2) 0.90097(2) 0.96767(2) 0.39168(2) 0 0.40822(3) 0.71311(3) 0 0.76223(3) 0.14473(4)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.30101(5) 0.92061(5) 0.46935(5) 0.36376(4) 0.84920(4) 0.08867(4) 0.36479(4) 0.14085(4) 0.63869(4) 1/2 0.04866(7) 0.43502(6) 1/2 0.08366(7) 0.28086(7)
95(1) 92(1) 102(1) 83(1) 85(1) 86(1) 98(1) 100(1) 95(1) 142(3) 82(1) 81(1) 142 81(1) 88(1)
Table 3 (continued ) Atom
Wyck. Occ.
x
y z
In6 In7 In8 In9 In10 In11 In12
4i 4i 4i 4i 4i 4i 4i
0.04401(4) 0.94415(3) 0.32645(4) 0.87633(3) 0.47076(3) 0.42976(5) 0.72752(4)
0 0 0 0 0 0 0
1.00 1.00 1.00 1.00 1.00 1.00 1.00
Ueq
0.33668(7) 116(2) 0.93713(7) 94(2) 0.28114(7) 106(2) 0.16950(7) 86(1) 0.82274(7) 90(2) 0.49548(7) 168(2) 0.24553(7) 87(1)
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.
at the heights y ¼ 0 and 1/2, and are displaced relative to each other along the [100] direction by the distance of a/2 (C-centered unit cell). The layers are built up by three-, four- and five-membered rings. Thus, the atoms of the largest size (RE) are situated only in pentagonal prisms, the atoms of medium size (In) are distributed in pentagonal and tetragonal ones, and the atoms of the smallest size (Pt) are placed in part of the trigonal prisms, while the other part of trigonal prisms remains empty. Two platinum atoms in Nd6Pt13In22 (Pt7 in the 2c site) are placed in distorted square prisms. The latter are substituted by two indium atoms (In3 in the 2c site) in Tb6Pt12In23. Similar layers, which are build up by three-, four- and five-membered rings, are characteristic of other ternary indides in the RE–Pt–In systems—RE4Pt10In21 [8], Ce6Pt11In14 [13], or REPt2In2 [14]. The most similar structure is Yb2Pd6In13 [15], in which we can single out fragments identical to those in the Nd6Pt13In22 structure (Fig. 1b). On the other hand, we can describe the structure of Nd6Pt13In22 as a packing of trigonal prisms, which form columns along the [010] direction (Fig. 2a). Therein we can single out two different types of chains formed by trigonal prisms, which differ in the way they are connected within the chain—either by means of double empty trigonal prisms or by means of distorted empty octahedra. The latter connect the adjoining chains at various heights. A similar type of packing trigonal prisms can also be observed in the Yb2Pd6In13 structure (Fig. 2b). The shortest interatomic distances in the Nd6Pt13In22 structure occur for Pt–In (269–307 pm) and In–In (294–372 pm). Each platinum atoms has at least 4–7 indium neighbors at Pt–In distances smaller than 287 pm. These Pt–In bond lengths are close to the sum of the covalent radii of 279 pm [16]. Also, the 12 crystallographically independent indium atoms have between 2 and 6 shorter In–In contacts that are equal or shorter than the shortest In–In distance of 325 pm in tetragonal body-centered indium [9]. Together, the platinum and indium atoms build up a complex threedimensional [Pt13In22] polyanionic network in which the neodymium atoms fill distorted pentagonal and hexagonal channels (Fig. 3). This is the typical structural arrangement
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Table 4 Interatomic distances (pm), calculated with the single crystal lattice parameters of Nd6Pt13In22 Nd1:
Nd2:
Nd3:
Pt1:
Pt2:
2 1 2 2 1 2 1 1 1 2 2 2 2 2 2 1 1 1 1 1 2 2 2 1 2 2 1 1 1 2 1 1 1 2 2 1 1 2 2 1 2 1
Pt4 In11 In9 In6 In10 Pt5 In11 In1 In8 Pt7 Pt2 In4 In12 In1 Pt3 In7 In4 In9 In5 Pt4 Pt1 In2 Pt6 In2 In11 In8 In6 In5 In12 In12 In2 In8 In5 In2 Nd3 In10 In1 In7 In5 In12 Nd2 Pt6
300.2 316.8 319.9 322.9 327.5 338.9 343.6 348.2 348.9 353.6 319.5 321.0 321.2 331.8 335.9 338.7 343.1 343.8 349.1 278.3 321.0 321.8 326.9 334.5 342.7 349.3 350.3 353.2 357.2 272.8 277.8 279.6 282.1 284.4 321.0 268.8 276.9 282.8 284.3 284.9 319.5 326.2
Pt3:
Pt4:
Pt5:
Pt6:
Pt7:
In1:
2 2 1 1 1 2 1 1 1 2 2 2 2 1 2 1 1 1 2 1 1 1 2 2 1 2 2 4 2 4 1 1 2 2 2 1 2 1
In9 In4 In4 In1 In8 Nd2 In9 Pt7 Nd3 In11 In8 Nd1 In10 In9 In1 In7 In6 In7 Nd1 In11 In2 In10 In6 In5 Pt2 Nd3 Pt4 In11 In6 Nd1 Pt3 Pt2 Pt5 In7 In9 In10 Nd2 Nd1
270.5 273.0 273.9 276.8 278.8 335.9 272.5 275.4 278.3 287.8 299.2 300.2 273.4 277.2 278.8 284.0 293.9 307.0 338.9 275.3 275.8 277.7 279.1 287.4 326.2 326.9 275.4 285.9 304.4 353.6 276.8 276.9 278.8 315.3 319.5 321.8 331.8 348.2
In2:
In4:
In5:
In6:
In7:
1 1 2 1 2 2 2 1 2 1 1 1 2 2 1 2 1 2 2 2 1 1 2 1 1 2 2 1 1 2 2 2 1 1 2 1 1 2 1 2 1 1
Pt6 Pt1 Pt1 In12 In2 Nd3 In5 Nd3 Pt3 Pt3 In12 In9 In4 Nd2 Nd2 In8 Pt1 Pt2 Pt6 In2 In7 In6 In12 Nd2 Nd3 In10 Pt6 Pt5 Pt7 In11 In10 Nd1 In5 Nd3 Pt2 Pt5 In7 In10 Pt5 In1 In5 Nd2
275.8 277.8 284.4 298.0 315.6 321.8 324.6 334.5 273.0 273.9 293.9 295.8 320.2 321.0 343.1 355.7 282.1 284.3 287.4 324.6 325.1 325.1 341.7 349.1 353.2 371.6 279.1 293.9 304.4 315.7 317.4 322.9 325.1 350.3 282.8 284.0 297.5 304.1 307.0 315.3 325.0 338.7
In8:
In9:
In10:
In11:
In12:
1 1 2 2 2 1 2 1 2 2 1 1 1 2 2 2 1 1 2 1 2 2 1 1 2 1 2 2 2 1 2 1 1 1 2 1 1 1 2 2 2 1
Pt3 Pt1 Pt4 In9 In12 Nd1 Nd3 In11 In4 Pt3 Pt4 Pt5 In4 In1 Nd1 In8 Nd2 Pt2 Pt5 Pt6 In7 In6 In1 Nd1 In5 Pt6 Pt7 Pt4 In6 Nd1 Nd3 Nd1 In8 In11 Pt1 Pt2 In4 In2 Nd2 In5 In8 Nd3
278.8 279.6 299.2 337.1 342.1 348.9 349.3 352.8 355.7 270.5 272.5 277.2 295.8 319.5 319.9 337.1 343.8 268.8 273.4 277.7 304.1 317.4 321.8 327.5 371.6 275.3 285.9 287.8 315.7 316.8 342.6 343.7 352.8 363.2 272.8 284.9 293.9 298.0 321.2 341.7 342.1 357.2
Standard deviations are all equal or less than 0.2 pm. All distances within the first coordination spheres are listed.
observed for a whole family of rare earth-transition metalindides [1]. The three crystallographically independent neodymium sites have high coordination numbers, i.e. CN 15 (6 Pt+9 In) for Nd1, CN 14 (4 Pt+10 In) for Nd2, and CN 15 (5 Pt+10 In) for Nd3 (Fig. 4). This is the typical coordination for rare earth metal atoms in such intermetallic rare earth indides [1]. Nd1 and Nd3 have a distorted penta-capped pentagonal-prismatic coordination. The Nd2 coordination sphere is similar, but the In8 atoms (the 15th neighbor), coordinating the fifth rectangular site of the pentagonal prisms have the long Nd2–In8 distance of 408 pm. The shortest Nd–Nd distance is at 442 pm and corresponds to the b lattice parameter. In view of the average Nd–Nd distance of 367 pm in the ABAC stacking
variant of neodymium [9], we do not consider the Nd–Nd distances in Nd6Pt13In22 as bonding. The difference between the structures of Nd6Pt13In22 presented here and Tb6Pt12In23 [6] is the occupancy of the 2c site. The latter is fully occupied by indium in Tb6Pt12In23, but with platinum in Nd6Pt13In22. The crystals with samarium and gadolinium as rare earth metal component revealed mixed Pt–In occupancies, leading to the refined compositions Sm6Pt12.30In22.70, and Gd6 Pt12.48In22.52 for the crystals investigated. This situation of transition metal and/or indium/gallium occupancy has also been observed in the series of U4Ni11Ga20 [17] and Ho4Ni10Ga21 [18]-type gallides and indides [8,19–21]. In Fig. 5 we present cutouts of these structures in order to elucidate the crystal chemical
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Fig. 3. View of the Nd6Pt13In22 structure along the short unit cell axis. Neodymium, platinum, and indium atoms are drawn as gray, black filled, and open circles, respectively. The three-dimensional [Pt13In22] network is emphasized. For clarity, only the Pt–In and Pt–Pt bonds are drawn.
Fig. 1. (a). Projection of the Nd6Pt13In22 structure onto the xz plane. Neodymium, platinum, and indium atoms are drawn as gray, black filled, and open circles, respectively. All atoms lie on mirror planes at y ¼ 0 (thin lines) and y ¼ 1/2 (thick lines), respectively. (b). Projection of the Yb2Pd6In13 structure onto the xz plane. Common fragments of these structures are emphasized.
Fig. 2. Packing of the trigonal prisms and octahedra in the Nd6Pt13In22 (a) and Yb2Pd6In13 (b) structures. The empty trigonal double prisms and octahedra are shaded.
Fig. 4. Coordination polyhedra of the neodymium atoms in Nd6Pt13In22. Neodymium, platinum, and indium atoms are drawn as gray, black filled, and open circles, respectively. Nd1, Nd2, and Nd3 have site symmetry m.
consequences of the different occupancies. In the Nd6Pt13In22 structure the platinum atoms build a linear chain with a Pt–Pt distance of 275 pm, close to the Pt–Pt distance of 277 pm in fcc platinum [9]. We can thus assume a significant degree of Pt–Pt bonding in Nd6Pt13In22. The linear Pt3 chains (one-dimensional clusters) are connected via the In11 atoms. In the structures of Y4Ni11In20 [21] and Nd4Pd10In21 [20], the different occupancy in the nickel compound leads to a one-dimensional cluster unit. The Ni6 atoms are condensed with two Ni12 pairs, while the In1 atoms in Nd4Pd10In21 connect the Pd22 dumb-bells. Finally we need to discuss the course of the lattice parameters a, b, and c (Table 1). Since platinum (129 pm) and indium (150 pm) [16] have significantly different covalent radii, the occupancy of the 2c site strongly influences the a and c lattice parameters. The b lattice parameter, on the other hand, is more or less determined by the size of the rare earth element (Table 1). If the 2c site is occupied by the larger indium atoms, as in the case of Tb6Pt12In23, the a lattice parameter significantly expands, in order to realize longer In3–In11 distances of 304 pm, as compared to the smaller Pt7–In11 distances of 286 pm in Nd6Pt13In22. As a consequence to this enlargement, the c lattice parameter contracts, in order to retain the other distances.
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References
Fig. 5. Coordination of the 2c site in the Nd6Pt13In22 and Tb6Pt12In23 structure and of the 2b and 2d sites of Nd4Pt10In21 and Y4Ni11In20, respectively. The rare earth metal, transition metal, and indium atoms are drawn as grey, black filled, and open circles, respectively. For details see text.
Acknowledgments We are grateful to Dr. R.-D. Hoffmann for help with the intensity data collections. This work was supported by the Deutsche Forschungsgemeinschaft. V.I.Z. is indebted to the Alexander-von-Humboldt Foundation for a research stipend.
[1] Ya.M. Kalychak, V.I. Zaremba, R. Po¨ttgen, M. Lukachuk, R.-D. Hoffmann, Rare earth-transition metal-indides, in: K.A. Gschneider Jr., V.K. Pecharsky, J.-C. Bu¨nzli (Eds.), Handbook on the Physics and Chemistry of Rare Earths, vol. 34, Elsevier, Amsterdam, 2005, pp. 1–133 (Chapter 218). [2] M.G. Kanatzidis, R. Po¨ttgen, W. Jeitschko, Angew. Chem. 117 (2005) 7156. [3] Ya.V. Galadzhun, R. Po¨ttgen, Z. Anorg. Allg. Chem. 625 (1999) 481. [4] U.Ch. Rodewald, V.I. Zaremba, Ya.V. Galadzhun, R.-D. Hoffmann, R. Po¨ttgen, Z. Anorg. Allg. Chem. 628 (2002) 2293. [5] M.F. Hundley, J.L. Sarrao, J.D. Thompson, R. Movshovich, M. Jaime, C. Petrovic, Z. Fisk, Phys. Rev. B 65 (2002) 024401. [6] V.I. Zaremba, Ya.M. Kalychak, V.P. Dubenskiy, R.-D. Hoffmann, U. Ch. Rodewald, R. Po¨ttgen, J. Solid State Chem. 169 (2002) 118. [7] V.I. Zaremba, U.Ch. Rodewald, R.-D. Hoffmann, Ya.M. Kalychak, R. Po¨ttgen, Z. Anorg. Allg. Chem. 629 (2003) 1157. [8] V.I. Zaremba, V. Hlukhyy, U.Ch. Rodewald, R. Po¨ttgen, Z. Anorg. Allg. Chem. 631 (2005) 1371. [9] J. Donohue, The Structures of the Elements, Wiley, New York, 1974. [10] R. Po¨ttgen, Th. Gulden, A. Simon, GIT-Laborfachzeitschrift 43 (1999) 133. [11] K. Yvon, W. Jeitschko, E. Parthe´, J. Appl. Crystallogr. 10 (1977) 73. [12] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, University of Go¨ttingen, Germany, 1997. [13] J. Stepien´-Damm, Z. Bukowski, V.I. Zaremba, A.P. Pikul, D. Kaczorowski, J. Alloy Compd. 379 (2004) 204. [14] V.I. Zaremba, Ya. Galadzhun, Ya. Kalychak, D. Kaczorowski, J. Stepien´-Damm, J. Alloy Compd. 296 (2000) 280. [15] V.I. Zaremba, V.P. Dubenskiy, Ya.M. Kalychak, R.-D. Hoffmann, R. Po¨ttgen, Solid State Sci. 4 (2002) 1293. [16] J. Emsley, The Elements, Oxford University Press, Oxford, 1999. [17] Yu.N. Grin, P. Rogl, J. Nucl. Mater. 137 (1986) 89. [18] Yu.N. Grin, Ya.P. Yarmolyuk, E.I. Gladyshevskii, Dokl. AN SSSR 245 (1979) 1102 (in Russian). [19] L. Vasylechko, W. Schnelle, U. Burkhardt, R. Ramlau, R. Niewa, H. Borrmann, K. Hiebl, Z. Hu, Yu. Grin, J. Alloy Compd. 350 (2003) 9. [20] V.I. Zaremba, U.Ch. Rodewald, Ya.M. Kalychak, Ya.V. Galadzhun, D. Kaczorowski, R.-D. Hoffmann, R. Po¨ttgen, Z. Anorg. Allg. Chem. 629 (2003) 434. [21] V. Hlukhyy, V.I. Zaremba, Ya.M. Kalychak, R. Po¨ttgen, J. Solid State Chem. 177 (2004) 1359.
Journal of Solid State Chemistry 179 (2006) 891–897 www.elsevier.com/locate/jssc
Synthesis and crystal structures of Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 Vasyl I. Zarembaa, Vitaliy P. Dubenskiya, Ute Ch. Rodewaldb, Birgit Heyingb, Rainer Po¨ttgenb, a
Inorganic Chemistry Department, Ivan Franko National University of Lviv, Kyryla and Mephodiya Street 6, 79005 Lviv, Ukraine b Institut fu¨r Anorganische und Analytische Chemie, Universita¨t Mu¨nster, Corrensstrasse 36, D-48149 Mu¨nster, Germany Received 26 October 2005; received in revised form 6 December 2005; accepted 10 December 2005 Available online 20 January 2006
Abstract The rare earth-platinum-indides Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 were synthesized from the elements by arcmelting of the components. Single crystals were grown using special annealing sequences. The three indides were investigated by X-ray powder and single crystal diffraction: Tb6Pt12In23 type, C2/m, Z ¼ 2, a ¼ 2811:9ð6Þ, b ¼ 441:60ð9Þ, c ¼ 1486:6ð3Þ pm, b ¼ 112:10ð3Þ1, wR2 ¼ 0.0629, 3645 F2 values, 126 variables for Nd6Pt13In22, a ¼ 2821:9ð6Þ, b ¼ 443:06ð9Þ, c ¼ 1481:0ð3Þ pm, b ¼ 112:39ð3Þ1, wR2 ¼ 0.0543, 3679 F2 values, 127 variables for Sm6Pt12.30In22.70, and a ¼ 2818:5ð6Þ, b ¼ 439:90ð9Þ, c ¼ 1480:9ð3Þ pm, b ¼ 112:29ð3Þ1, wR2 ¼ 0.0778, 3938 F2 values, 127 variables for Gd6Pt12.48In22.52. Most platinum atoms in these structures have a distorted trigonal prismatic coordination by rare earth metal and indium atoms. Together, the platinum and indium atoms build up a complex threedimensional [Pt12+xIn23x] polyanionic network in which the rare earth metal atoms fill distorted pentagonal and hexagonal channels. The 2c Wyckoff site in these structures plays a peculiar role. This site is occupied by indium in the prototype Tb6Pt12In23, while platinum atoms fill the 2c site in Nd6Pt13In22, leading to a linear Pt3 chain with Pt–Pt distances of 275 pm. The crystals with samarium and gadolinium as rare earth metal component show mixed Pt/In occupancies. r 2005 Elsevier Inc. All rights reserved. Keywords: Intermetallic compounds; Crystal structure; Indium
1. Introduction High-quality single crystals of indium-rich (more than 50 at% per formula unit) rare earth (RE)-transition metal (T)-indides can be grown via indium flux techniques. Either the elements are reacted directly with an excess of indium, or a precursor alloy is re-crystallized from liquid indium via a special temperature program. The excess indium can softly be removed with diluted acetic acid. An overview on the different compounds and metal flux techniques is given in [1] and [2]. In the RE–Pt–In systems, the indium-rich compounds REPtIn3 (RE ¼ La, Ce, Pr, Nd, Sm) [3], RE3Pt4In12 Corresponding author. Fax: +49 251 83 36002.
E-mail addresses: [email protected] (V.I. Zaremba), [email protected] (R. Po¨ttgen). 0022-4596/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2005.12.022
(RE ¼ Gd, Tb) [4], RE3Pt4In13 (RE ¼ La, Ce) [5], Dy2 Pt7In16 and Tb6Pt12In23 [6], LaPtIn4 and YbPtIn4 [3,7], and RE4Pt10In21 (RE ¼ La, Ce, Pr, Nd) [8] have been synthesized via the indium-flux technique or through special annealing procedures. All these compounds have complex crystal structures, where the platinum and indium atoms build up three-dimensional polyanionic networks. Within the polyanionic networks, the platinum atoms are well separated from each other. The shortest Pt–Pt distances observed are in Gd3Pt4In12 (338 pm) [4] and Tb6Pt12In23 (320 pm) [6], however, these Pt–Pt distances are considerably longer than the Pt–Pt distance of 277 pm in fcc platinum [9]. Further phase analytical investigations in the RE–Pt–In systems revealed a peculiar crystal chemical situation for the Tb6Pt12In23 structure type. The 2c In3 site can also be occupied by platinum (leading to a Pt3 cluster unit) or one observes Pt/In mixing. Both
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Table 1 Lattice parameters of the monoclinic indides RE6Pt12+xIn23x Compound
a (pm)
b (pm)
c (pm)
b (deg)
V (nm3)
Ref.
Nd6Pt13In22a Nd6Pt13In22 Sm6Pt12.30In22.70a Sm6Pt12In23 Gd6Pt12.48In22.52a Gd6Pt12In23 Tb6Pt12In23
2811.9(6) 2812.7(5) 2821.9(6) 2820.5(5) 2818.5(6) 2814.2(3) 2834.6(4)
441.60(9) 441.7(1) 443.06(9) 443.3(1) 439.90(9) 437.82(6) 440.05(7)
1486.6(3) 1487.2(3) 1481.0(3) 1480.7(3) 1480.9(3) 1479.9(1) 1477.1(3)
112.10(3) 112.11(2) 112.39(3) 112.36(1) 112.29(3) 112.035(9) 112.37(1)
1.7104 1.7119 1.7121 1.7121 1.6990 1.6902 1.7038
This This This This This This [6]
a
work work work work work work
Single crystal data.
Table 2 Crystal data and structure refinement for RE6Pt12+xIn23x (RE ¼ Nd, Sm and Gd) with Tb6Pt12In23-type structure, space group C2/m; Z ¼ 2 Empirical formula
Nd6Pt13In22
Sm6Pt12.30(1)In22.70(1)
Gd6Pt12.48(1)In22.52(1)
Molar mass (g/mol) Unit cell dimensions Calculated density (g/cm3) Crystal size (mm3) Detector distance (mm) Exposure time (min) o range; increment Integr. param. A, B, EMS Transm. ratio (max/min) Absorption coefficient (mm1) F(000) y range (deg) Range in hkl Total no. reflections Independent reflections Reflections with I42sðIÞ Data/parameters Goodness-of-fit on F2 Weighting schemea
5927.65 Table 1 11.51 15 15 170 70 8 24–1661; 1.01 14.0; 4.0; 0.012 5.12 76.3 4904 3–34 43/+25, 76, 722 8537 3645 (Rint ¼ 0.0490) 2873 (Rs ¼ 0.0515) 3645/126 0.942 a ¼ 0.0296 b¼0 R1 ¼ 0.0326 wR2 ¼ 0.0595 R1 ¼ 0.0495 wR2 ¼ 0.0629 0.00045(1) 2.66/3.73
5964.31 Table 1 11.57 15 20 80 70 12 0–1801; 1.01 14.5; 4.5; 0.012 6.67 77.4 4928 3–34 743, 76, 722 11 660 3679 (Rint ¼ 0.0670) 2552 (Rs ¼ 0.0781) 3679/127 0.889 a ¼ 0.0157 b¼0 R1 ¼ 0.0362 wR2 ¼ 0.0488 R1 ¼ 0.0710 wR2 ¼ 0.0543 0.000235(7) 2.91/4.74
6005.71 Table 1 11.74 15 15 140 70 5 0–1801; 1.01 13.5; 3.5; 0.012 7.72 79.3 4952 3–35 744, 76, 723 12 855 3938 (Rint ¼ 0.0652) 3266 (Rs ¼ 0.0530) 3938/127 1.001 a ¼ 0.0397 b¼0 R1 ¼ 0.0367 wR2 ¼ 0.0734 R1 ¼ 0.0485 wR2 ¼ 0.0778 0.00041(2) 3.33/–5.83
Final R indices [I42sðIÞ] R indices (all data) Extinction coefficient Largest diff. peak and hole (e/A˚3) a
Weight ¼ 1/[s
2
(F2o)+(aP)2+bP] where P ¼ 1=3 max (0, F2o)+2/3 F2c .
situations have been observed in the indides Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52. The synthesis, structure refinements, and crystal chemistry of these compounds are reported herein. 2. Experimental 2.1. Synthesis Starting materials for the preparation of Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 were ingots of the rare earth metals (Kelpin, Chempur or Johnson-Matthey), platinum powder (ca. 200 mesh, Degussa-Hu¨ls), and
indium tear drops (Johnson-Matthey), all with stated purities better then 99.9%. In the first step the larger rare earth ingots were cut into smaller pieces under paraffin oil. They were subsequently washed with n-hexane and kept under argon atmosphere prior to use. The paraffin oil and n-hexane were dried over sodium wire. The argon was purified before over titanium sponge (900 K), silica gel, and molecular sieves. The rare earth pieces were then arc-melted to small buttons under an argon atmosphere of ca. 600 mbar argon in a small arc-melting furnace [10]. Subsequently, the melted rare earth buttons were mixed with coldpressed pellets of the platinum powder and pieces of
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the indium tear drops in the ideal 6:12:23 or 6:13:22 atomic ratios and arc-melted. Each sample was re-melted three times in order to ensure good homogeneity. Weight losses after the melting procedures were always smaller than 0.5 wt%. After the arc-melting procedure the RE6Pt12In23 indides were obtained only as polycrystalline powders. Single crystals were grown using special heat treatment. First, the alloys were powdered and cold-pressed into pellets. Next, the samples were put in small tantalum containers that have been sealed in evacuated silica tubes as an oxidation protection. The ampoules were first heated to 1300 K for the Nd compound (to 1320 K for the Sm and Gd compounds) within 6 h and held at that temperature for another 6 h. Subsequently, the temperature was lowered at a rate of 4 K/h to 900 K for the Nd compound (to 920 K for the Sm and Gd compounds), then at a rate of 10 K/h to 700 K, and finally cooled to room temperature within 10 h. After cooling, the samples could easily be separated from the tantalum container. No reaction of the samples with tantalum could be detected. The brittle samples were all stable in air as compact pieces as well as fine-grained powders. The needle-shaped single crystals exhibit metallic luster. 2.2. X-ray powder diffraction The indides were investigated via Guinier powder patterns (imaging plate technique, Fujifilm BAS-1800) using CuKa1 radiation and a-quartz (a ¼ 491.30, c ¼ 540.46 pm) as an internal standard. The monoclinic lattice parameters (Table 1) were obtained from leastsquare fits of the Guinier powder data using a selfwritten computer program. The indexing of the complex powder patterns was facilitated through intensity calculations [11] using the positional parameters of the structure refinements. The lattice parameters determined from the powders and the single crystals showed reasonable agreement within two combined standard uncertainties. The course of the lattice parameters with respect to the rare earth metal component is discussed below. 2.3. Scanning electron microscopy The crystals investigated on the diffractometer have been analyzed in a scanning electron microscope (LEICA 420i) through energy dispersive analyses of X-rays using NdF3, SmF3, GdF3, platinum metal, and InAs were used as standards. No impurity elements heavier than sodium have been observed. The experimentally determined compositions of 1472 at% Nd:3372 at% Pt:5372 at% In for Nd6Pt13In22 (14.6:31.7:53.7), 1572 at% Sm:3072 at% Pt:5572 at% In for Sm6Pt12.3In22.7 (14.6:30.0:55.4), and 1572 at% Gd:3072 at% Pt:5572 at% In for Gd6Pt12.48In22.52 (14.6:30.4:55.0) were close to the compositions calculated from the structure refinements (in
893
parentheses). The uncertainties of the measurements of 72 at% arise from the irregular surface of the single crystals. 2.4. Structure refinements Needle-shaped single crystals of the three indides were selected from the crushed samples and examined on a Buerger precession camera (white Mo radiation, Fujifilm BAS-1800 imaging plate system) in order to check the quality. The intensity data sets were recorded in oscillation mode by use of a Stoe IPDS-II diffractometer with graphite monochromatized MoKa radiation. The absorption corrections for these crystals were numerical (X-Shape/X-Red). All relevant crystallographic data and experimental details for the data collections are listed in Table 2. The close structural relationship of the three new compounds with the Tb6Pt12In23 type was already evident from the X-ray powder data. Analyses of the diffractometer data sets were compatible with space group C2/m. The atomic parameters of Tb6Pt12In23 [6] were taken as starting values and the structures were refined with SHELXL-97 (full-matrix least-squares on F2) [12] with anisotropic displacement parameters for all atoms. The refinements revealed very small equivalent isotropic displacement parameters for the 2c Wyckoff site, indicating a larger scattering power. From a crystal chemical point of view, it is only possible to substitute the indium atoms of the Tb6Pt12In23 type by platinum. Refinement of the occupancy parameters of the 2c sites revealed full platinum occupancy for the neodymium crystal and Pt/In mixing for the samarium and the gadolinium crystals, leading to the refined compositions Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 for the crystals investigated. The final difference Fourier syntheses were flat for all three data sets (Table 2). The highest residual peaks were close to the platinum sites and most likely resulted from incomplete absorption corrections of these highly absorbing compounds. The positional parameters and interatomic distances of the refinements are listed in Tables 3 and 4. Further data on the structure refinements are available.1 3. Discussion The three new indides Nd6Pt13In22, Sm6Pt12.30In22.70, and Gd6Pt12.48In22.52 have a close structural relationship with the recently reported structure of Tb6Pt12In23 [6]. As an example we present a projection of the Nd6Pt13In22 structure onto the xz plane in Fig. 1a. The unit cell is formed by two identical networks situated 1 Details may be obtained from: Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany), by quoting the Registry Nos. CSD–415864 (Nd6Pt13In22), CSD–415865 (Sm6Pt12.30In22.70), and CSD–415866 (Gd6Pt12.48In22.52).
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Table 3 Atomic coordinates and isotropic displacement parameters (pm2) of RE6Pt12+xIn23x (RE ¼ Nd, Sm and Gd) Atom
Wyck. Occ.
x
y z
Ueq
Nd6Pt13In22 Nd1 Nd2 Nd3 Pt1 Pt2 Pt3 Pt4 Pt5 Pt6 Pt7 In1 In2 In4 In5 In6 In7 In8 In9 In10 In11 In12
4i 4i 4i 4i 4i 4i 4i 4i 4i 2c 4i 4i 4i 4i 4i 4i 4i 4i 4i 4i 4i
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
0.45324(3) 0.82120(3) 0.83717(3) 0.25147(2) 0.38141(2) 0.32036(2) 0.90101(2) 0.96735(2) 0.39324(2) 0 0.40842(4) 0.71263(4) 0.76225(4) 0.14323(4) 0.04265(4) 0.94468(4) 0.32556(4) 0.87577(4) 0.47078(4) 0.43497(4) 0.72748(4)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.30004(5) 84(1) 0.91931(5) 82(1) 0.46918(5) 81(1) 0.36333(3) 79(1) 0.84816(3) 83(1) 0.08900(3) 78(1) 0.36453(3) 95(1) 0.13891(4) 95(1) 0.63812(3) 83(1) 1/2 161(2) 0.04752(6) 78(2) 0.43517(6) 76(2) 0.08371(6) 77(2) 0.28181(6) 84(2) 0.33970(7) 90(2) 0.93590(6) 92(2) 0.27999(6) 102(2) 0.16870(6) 80(2) 0.82143(6) 88(2) 0.49771(6) 95(2) 0.24700(6) 83(2)
Sm6Pt12.30(1)In22.70(1) Sm1 Sm2 Sm3 Pt1 Pt2 Pt3 Pt4 Pt5 Pt6 Pt7 In1 In2 In3 In4 In5 In6 In7 In8 In9 In10 In11 In12
4i 4i 4i 4i 4i 4i 4i 4i 4i 2c 4i 4i 2c 4i 4i 4i 4i 4i 4i 4i 4i 4i
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.30(1) 1.00 1.00 0.70 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
0.45384(3) 0.82103(3) 0.83509(3) 0.25192(2) 0.38150(2) 0.32044(2) 0.90060(2) 0.96696(2) 0.39235(2) 0 0.40768(4) 0.71267(4) 0 0.76219(4) 0.14465(4) 0.04421(4) 0.94407(4) 0.32552(4) 0.87620(4) 0.47191(4) 0.42752(5) 0.72735(4)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.30123(6) 0.92033(6) 0.46980(6) 0.36348(4) 0.84887(4) 0.09017(4) 0.36520(4) 0.13908(5) 0.64141(4) 1/2 0.04810(8) 0.43431(8) 1/2 0.08352(8) 0.28019(8) 0.33298(8) 0.93705(8) 0.28111(8) 0.16946(8) 0.82561(8) 0.49530(9) 0.24589(8)
95(2) 93(2) 104(2) 87(1) 88(1) 89(1) 106(1) 103(1) 98(1) 138(5) 89(2) 90(1) 138 88(2) 91(2) 114(2) 99(2) 117(2) 93(2) 94(2) 165(3) 91(2)
Gd6Pt12.48(1)In22.52(1) Gd1 Gd2 Gd3 Pt1 Pt2 Pt3 Pt4 Pt5 Pt6 Pt7 In1 In2 In3 In4 In5
4i 4i 4i 4i 4i 4i 4i 4i 4i 2c 4i 4i 2c 4i 4i
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.48(1) 1.00 1.00 0.52 1.00 1.00
0.45386(2) 0.82141(2) 0.83570(2) 0.25268(2) 0.38104(2) 0.32048(2) 0.90097(2) 0.96767(2) 0.39168(2) 0 0.40822(3) 0.71311(3) 0 0.76223(3) 0.14473(4)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0.30101(5) 0.92061(5) 0.46935(5) 0.36376(4) 0.84920(4) 0.08867(4) 0.36479(4) 0.14085(4) 0.63869(4) 1/2 0.04866(7) 0.43502(6) 1/2 0.08366(7) 0.28086(7)
95(1) 92(1) 102(1) 83(1) 85(1) 86(1) 98(1) 100(1) 95(1) 142(3) 82(1) 81(1) 142 81(1) 88(1)
Table 3 (continued ) Atom
Wyck. Occ.
x
y z
In6 In7 In8 In9 In10 In11 In12
4i 4i 4i 4i 4i 4i 4i
0.04401(4) 0.94415(3) 0.32645(4) 0.87633(3) 0.47076(3) 0.42976(5) 0.72752(4)
0 0 0 0 0 0 0
1.00 1.00 1.00 1.00 1.00 1.00 1.00
Ueq
0.33668(7) 116(2) 0.93713(7) 94(2) 0.28114(7) 106(2) 0.16950(7) 86(1) 0.82274(7) 90(2) 0.49548(7) 168(2) 0.24553(7) 87(1)
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.
at the heights y ¼ 0 and 1/2, and are displaced relative to each other along the [100] direction by the distance of a/2 (C-centered unit cell). The layers are built up by three-, four- and five-membered rings. Thus, the atoms of the largest size (RE) are situated only in pentagonal prisms, the atoms of medium size (In) are distributed in pentagonal and tetragonal ones, and the atoms of the smallest size (Pt) are placed in part of the trigonal prisms, while the other part of trigonal prisms remains empty. Two platinum atoms in Nd6Pt13In22 (Pt7 in the 2c site) are placed in distorted square prisms. The latter are substituted by two indium atoms (In3 in the 2c site) in Tb6Pt12In23. Similar layers, which are build up by three-, four- and five-membered rings, are characteristic of other ternary indides in the RE–Pt–In systems—RE4Pt10In21 [8], Ce6Pt11In14 [13], or REPt2In2 [14]. The most similar structure is Yb2Pd6In13 [15], in which we can single out fragments identical to those in the Nd6Pt13In22 structure (Fig. 1b). On the other hand, we can describe the structure of Nd6Pt13In22 as a packing of trigonal prisms, which form columns along the [010] direction (Fig. 2a). Therein we can single out two different types of chains formed by trigonal prisms, which differ in the way they are connected within the chain—either by means of double empty trigonal prisms or by means of distorted empty octahedra. The latter connect the adjoining chains at various heights. A similar type of packing trigonal prisms can also be observed in the Yb2Pd6In13 structure (Fig. 2b). The shortest interatomic distances in the Nd6Pt13In22 structure occur for Pt–In (269–307 pm) and In–In (294–372 pm). Each platinum atoms has at least 4–7 indium neighbors at Pt–In distances smaller than 287 pm. These Pt–In bond lengths are close to the sum of the covalent radii of 279 pm [16]. Also, the 12 crystallographically independent indium atoms have between 2 and 6 shorter In–In contacts that are equal or shorter than the shortest In–In distance of 325 pm in tetragonal body-centered indium [9]. Together, the platinum and indium atoms build up a complex threedimensional [Pt13In22] polyanionic network in which the neodymium atoms fill distorted pentagonal and hexagonal channels (Fig. 3). This is the typical structural arrangement
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Table 4 Interatomic distances (pm), calculated with the single crystal lattice parameters of Nd6Pt13In22 Nd1:
Nd2:
Nd3:
Pt1:
Pt2:
2 1 2 2 1 2 1 1 1 2 2 2 2 2 2 1 1 1 1 1 2 2 2 1 2 2 1 1 1 2 1 1 1 2 2 1 1 2 2 1 2 1
Pt4 In11 In9 In6 In10 Pt5 In11 In1 In8 Pt7 Pt2 In4 In12 In1 Pt3 In7 In4 In9 In5 Pt4 Pt1 In2 Pt6 In2 In11 In8 In6 In5 In12 In12 In2 In8 In5 In2 Nd3 In10 In1 In7 In5 In12 Nd2 Pt6
300.2 316.8 319.9 322.9 327.5 338.9 343.6 348.2 348.9 353.6 319.5 321.0 321.2 331.8 335.9 338.7 343.1 343.8 349.1 278.3 321.0 321.8 326.9 334.5 342.7 349.3 350.3 353.2 357.2 272.8 277.8 279.6 282.1 284.4 321.0 268.8 276.9 282.8 284.3 284.9 319.5 326.2
Pt3:
Pt4:
Pt5:
Pt6:
Pt7:
In1:
2 2 1 1 1 2 1 1 1 2 2 2 2 1 2 1 1 1 2 1 1 1 2 2 1 2 2 4 2 4 1 1 2 2 2 1 2 1
In9 In4 In4 In1 In8 Nd2 In9 Pt7 Nd3 In11 In8 Nd1 In10 In9 In1 In7 In6 In7 Nd1 In11 In2 In10 In6 In5 Pt2 Nd3 Pt4 In11 In6 Nd1 Pt3 Pt2 Pt5 In7 In9 In10 Nd2 Nd1
270.5 273.0 273.9 276.8 278.8 335.9 272.5 275.4 278.3 287.8 299.2 300.2 273.4 277.2 278.8 284.0 293.9 307.0 338.9 275.3 275.8 277.7 279.1 287.4 326.2 326.9 275.4 285.9 304.4 353.6 276.8 276.9 278.8 315.3 319.5 321.8 331.8 348.2
In2:
In4:
In5:
In6:
In7:
1 1 2 1 2 2 2 1 2 1 1 1 2 2 1 2 1 2 2 2 1 1 2 1 1 2 2 1 1 2 2 2 1 1 2 1 1 2 1 2 1 1
Pt6 Pt1 Pt1 In12 In2 Nd3 In5 Nd3 Pt3 Pt3 In12 In9 In4 Nd2 Nd2 In8 Pt1 Pt2 Pt6 In2 In7 In6 In12 Nd2 Nd3 In10 Pt6 Pt5 Pt7 In11 In10 Nd1 In5 Nd3 Pt2 Pt5 In7 In10 Pt5 In1 In5 Nd2
275.8 277.8 284.4 298.0 315.6 321.8 324.6 334.5 273.0 273.9 293.9 295.8 320.2 321.0 343.1 355.7 282.1 284.3 287.4 324.6 325.1 325.1 341.7 349.1 353.2 371.6 279.1 293.9 304.4 315.7 317.4 322.9 325.1 350.3 282.8 284.0 297.5 304.1 307.0 315.3 325.0 338.7
In8:
In9:
In10:
In11:
In12:
1 1 2 2 2 1 2 1 2 2 1 1 1 2 2 2 1 1 2 1 2 2 1 1 2 1 2 2 2 1 2 1 1 1 2 1 1 1 2 2 2 1
Pt3 Pt1 Pt4 In9 In12 Nd1 Nd3 In11 In4 Pt3 Pt4 Pt5 In4 In1 Nd1 In8 Nd2 Pt2 Pt5 Pt6 In7 In6 In1 Nd1 In5 Pt6 Pt7 Pt4 In6 Nd1 Nd3 Nd1 In8 In11 Pt1 Pt2 In4 In2 Nd2 In5 In8 Nd3
278.8 279.6 299.2 337.1 342.1 348.9 349.3 352.8 355.7 270.5 272.5 277.2 295.8 319.5 319.9 337.1 343.8 268.8 273.4 277.7 304.1 317.4 321.8 327.5 371.6 275.3 285.9 287.8 315.7 316.8 342.6 343.7 352.8 363.2 272.8 284.9 293.9 298.0 321.2 341.7 342.1 357.2
Standard deviations are all equal or less than 0.2 pm. All distances within the first coordination spheres are listed.
observed for a whole family of rare earth-transition metalindides [1]. The three crystallographically independent neodymium sites have high coordination numbers, i.e. CN 15 (6 Pt+9 In) for Nd1, CN 14 (4 Pt+10 In) for Nd2, and CN 15 (5 Pt+10 In) for Nd3 (Fig. 4). This is the typical coordination for rare earth metal atoms in such intermetallic rare earth indides [1]. Nd1 and Nd3 have a distorted penta-capped pentagonal-prismatic coordination. The Nd2 coordination sphere is similar, but the In8 atoms (the 15th neighbor), coordinating the fifth rectangular site of the pentagonal prisms have the long Nd2–In8 distance of 408 pm. The shortest Nd–Nd distance is at 442 pm and corresponds to the b lattice parameter. In view of the average Nd–Nd distance of 367 pm in the ABAC stacking
variant of neodymium [9], we do not consider the Nd–Nd distances in Nd6Pt13In22 as bonding. The difference between the structures of Nd6Pt13In22 presented here and Tb6Pt12In23 [6] is the occupancy of the 2c site. The latter is fully occupied by indium in Tb6Pt12In23, but with platinum in Nd6Pt13In22. The crystals with samarium and gadolinium as rare earth metal component revealed mixed Pt–In occupancies, leading to the refined compositions Sm6Pt12.30In22.70, and Gd6 Pt12.48In22.52 for the crystals investigated. This situation of transition metal and/or indium/gallium occupancy has also been observed in the series of U4Ni11Ga20 [17] and Ho4Ni10Ga21 [18]-type gallides and indides [8,19–21]. In Fig. 5 we present cutouts of these structures in order to elucidate the crystal chemical
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Fig. 3. View of the Nd6Pt13In22 structure along the short unit cell axis. Neodymium, platinum, and indium atoms are drawn as gray, black filled, and open circles, respectively. The three-dimensional [Pt13In22] network is emphasized. For clarity, only the Pt–In and Pt–Pt bonds are drawn.
Fig. 1. (a). Projection of the Nd6Pt13In22 structure onto the xz plane. Neodymium, platinum, and indium atoms are drawn as gray, black filled, and open circles, respectively. All atoms lie on mirror planes at y ¼ 0 (thin lines) and y ¼ 1/2 (thick lines), respectively. (b). Projection of the Yb2Pd6In13 structure onto the xz plane. Common fragments of these structures are emphasized.
Fig. 2. Packing of the trigonal prisms and octahedra in the Nd6Pt13In22 (a) and Yb2Pd6In13 (b) structures. The empty trigonal double prisms and octahedra are shaded.
Fig. 4. Coordination polyhedra of the neodymium atoms in Nd6Pt13In22. Neodymium, platinum, and indium atoms are drawn as gray, black filled, and open circles, respectively. Nd1, Nd2, and Nd3 have site symmetry m.
consequences of the different occupancies. In the Nd6Pt13In22 structure the platinum atoms build a linear chain with a Pt–Pt distance of 275 pm, close to the Pt–Pt distance of 277 pm in fcc platinum [9]. We can thus assume a significant degree of Pt–Pt bonding in Nd6Pt13In22. The linear Pt3 chains (one-dimensional clusters) are connected via the In11 atoms. In the structures of Y4Ni11In20 [21] and Nd4Pd10In21 [20], the different occupancy in the nickel compound leads to a one-dimensional cluster unit. The Ni6 atoms are condensed with two Ni12 pairs, while the In1 atoms in Nd4Pd10In21 connect the Pd22 dumb-bells. Finally we need to discuss the course of the lattice parameters a, b, and c (Table 1). Since platinum (129 pm) and indium (150 pm) [16] have significantly different covalent radii, the occupancy of the 2c site strongly influences the a and c lattice parameters. The b lattice parameter, on the other hand, is more or less determined by the size of the rare earth element (Table 1). If the 2c site is occupied by the larger indium atoms, as in the case of Tb6Pt12In23, the a lattice parameter significantly expands, in order to realize longer In3–In11 distances of 304 pm, as compared to the smaller Pt7–In11 distances of 286 pm in Nd6Pt13In22. As a consequence to this enlargement, the c lattice parameter contracts, in order to retain the other distances.
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References
Fig. 5. Coordination of the 2c site in the Nd6Pt13In22 and Tb6Pt12In23 structure and of the 2b and 2d sites of Nd4Pt10In21 and Y4Ni11In20, respectively. The rare earth metal, transition metal, and indium atoms are drawn as grey, black filled, and open circles, respectively. For details see text.
Acknowledgments We are grateful to Dr. R.-D. Hoffmann for help with the intensity data collections. This work was supported by the Deutsche Forschungsgemeinschaft. V.I.Z. is indebted to the Alexander-von-Humboldt Foundation for a research stipend.
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